This invention relates to a rock anchor for use in full column adhesive bonding applications.
A problem with using a resin or grout to secure a rock anchor within a rock hole is that the resin, typically comprising of an adhesive resinous component and a catalytic component, needs to be adequately mixed for the resultant resin mixture to set with sufficient binding strength.
Hereinafter, the terms rock anchor and rock bolt are used interchangeably to describe a device which has an elongate body, and which is inserted into a hole drilled into a rock face, to stabilize the rock to prevent collapse or rock fall.
Moreover, the resin is an expensive consumable that is often wasted; introduced into the rock hole in cartridges in amounts surplus to requirement for the particular hole-size, resulting in resin leaking from the hole.
Resin cartridges are also often damaged during storage or transportation to site because of the delicate frangible nature of the cartridge membrane.
Also, there is no way of ensuring a full column bond i.e. the annular space between the anchor and the rock hole wall is completely filled with resin, with a number of resin cartridges, introduced into the rock hole ahead of the anchor. This is because some of the cartridges may only partially rupture, or not rupture at all, when the rock anchor is moved through the hole. Therefore insufficient resin is mixed or introduced into the annular space to fix the anchor in place. Allied to this problem is that the cartridge material may form an adhesive barrier to the anchor and resin, or resin and rock wall, interface, a problem known as finger gloving.
Another problem comes when resin cartridges are inserted ahead of a rock anchor trapping air in the blind end of the rock hole. When the cartridges rupture and the resin sets, air voids get trapped within the set resin at this end. It is critical that a leading portion of the rock anchor is properly bonded to the rock hole as the mass of the rock supported by the anchor is often effectively suspended from this portion of the rock anchor, bonded to the rock hole.
When a resin capsule is placed in a hollow rock bolt, in a configuration as described in ZA2003/04376, another problem is experienced. The thin plastics material making up the frangible capsule does not release its contents in a controlled manner. The capsule may buckle at any point there-along, causing a bottleneck or blockage in the cartridge lumen, preventing the resin contained behind this point from progressing to a capsule outlet. Furthermore, the material tends to bunch when compressed, by a pressing means, and is often forced into a mixing device at a leading end of the bolt thus clogging up the device. As a result, the mixing ratios of the two part resin components in the capsule cannot be controlled which can lead to the resin improperly setting.